1. Field of the Invention
The invention relates generally to an improved preamplifier for use typically with a photoconductive sensor array.
2. Description of the Related Art
A scanning imaging system comprises a sensor array typically having 50 to 500 sensors which scan a desired scene and produce output signals which are then used to generate a video display of the scanned scene. Typically, the output signals from the sensors are initially fed through preamplifiers. Until now, however, there were many drawbacks with the preamplifiers, including physical size and power consumption.
For example, ac-coupled, single ended amplifiers require a physically large ac coupling capacitor. In addition to its size, the capacitor is the most unreliable component in the circuit and degrades system performance in several ways. First, the capacitor increases the system's sensitivity to microphonics. Second, on low frequency signals such as a scan of the sky, the charge on the capacitor will leak causing a change in the video display when in fact the detectors have sensed no change. Third, capacitors require long recovery times after an input overdrive. Further, with an ac-coupled, single ended amplifier, the bias signals for the detector are typically supplied by a separate circuit.
Even the traditional low noise differential amplifier which is dc-coupled to the detectors has limitations, including its level of power consumption and cross-talk. It would be advantageous to reduce the power dissipated by the differential amplifier, as well as reducing the cross-talk that occurs between sensor outputs.
Until now, the physical size and power consumption of the preamplifiers prevented the location of the preamplifiers adjacent to the sensors. It would be advantageous to have a preamplifier that is smaller and consumes less power. Such a preamplifier could be located adjacent to the sensor array, thus reducing cabling costs and improving performance and reliability.